1. Field of the Invention
The present invention relates generally to methods for controlling the freezing capacity of freezing AC ice-water systems, and more particularly, to a method for controlling freezing capacity of a variable-frequency freezing AC ice-water system.
2. Description of Related Art
Generally, requirement end equipment (e.g. air conditioners, central air conditioning systems, freezers, refrigerators etc.) in business places or office buildings for temperature control require large power output to achieve a sufficient cooling effect. Split-type chillers may have the problems of insufficiency and high cost. Multiple requirement end equipment in a business place are usually connected to a rear end chiller and exchange heat with the chiller for achieving desired cooling effects. For example, freezers and refrigerators in a supermarket or a warehouse are connected to a rear end chiller so as to allow heat exchange to occur therebetween through a cooling fluid provided by the chiller, thereby achieving freezing and refrigerating effects.
In practice, the freezing capacity supply of the chiller is very high, which accordingly results in high electric power consumption. For example, a chiller in a supermarket supplies several tons to several hundreds of tons of freezing capacity, thus resulting in high electric power consumption and high cost. If the freezing capacity during startup of the chiller can be efficiently utilized and the number of startup and shutdown events can be reduced, the cost can be greatly reduced.
In order to save electric power consumption, a variable-frequency chiller is developed, wherein the operating frequency thereof varies with the freezing capacity supply so as to reduce electric power consumption and save cost. The reason is that the freezing capacity supply of the variable-frequency chiller is positively proportional to the operating frequency of the variable-frequency chiller, and the electric power consumption is positively proportional to the cube of the operating frequency. That is, the electric power consumption is positively proportional to the cube of the freezing capacity supply. FIG. 1 is a plot showing the relationship between the electric power consumption and the supply of the variable-frequency chiller. Referring to FIG. 1, when the supply of the variable-frequency chiller is half of the maximum supply, the electric power consumption is 12.5% of the maximum electric power consumption (as shown in curve A). However, along with continuing global warming, only using the above-described variable-frequency method cannot meet the high demand for carbon emission reduction.
Therefore, it is imperative to provide a method for controlling the freezing efficiency of a variable-frequency freezing AC ice-water system so as to overcome the above-described drawbacks.